Re: [Xen-devel] [PATCH for 4.7] Remove HVMMEM_mmio_write_dm from the public interface.

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Apr 28, 2016 at 01:00:57PM +0100, Andrew Cooper wrote:
> On 28/04/16 12:59, Wei Liu wrote:
> > On Thu, Apr 28, 2016 at 07:40:45PM +0800, Yu, Zhang wrote:
> >> Thanks Jan. And I admire your rigorous thought. :)
> >>
> >> On 4/28/2016 6:57 PM, Jan Beulich wrote:
> >>>>>> On 28.04.16 at 12:42, <george.dunlap@xxxxxxxxxx> wrote:
> >>>> On 28/04/16 11:22, Jan Beulich wrote:
> >>>>>>>> On 28.04.16 at 10:29, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> >>>>>> @@ -5529,7 +5527,7 @@ long do_hvm_op(unsigned long op,
> >>>> XEN_GUEST_HANDLE_PARAM(void) arg)
> >>>>>>             [HVMMEM_ram_rw]  = p2m_ram_rw,
> >>>>>>             [HVMMEM_ram_ro]  = p2m_ram_ro,
> >>>>>>             [HVMMEM_mmio_dm] = p2m_mmio_dm,
> >>>>>> -            [HVMMEM_mmio_write_dm] = p2m_mmio_write_dm
> >>>>>> +            [HVMMEM_unused] = p2m_invalid
> >>>>> Why don't you simply delete the old line, without replacement?
> >> Well, I did not delete the old line, because in my coming patch(the
> >> p2m renaming code), I'm planning to introduce the HVMMEM_ioreq_server,
> >> which is HVMMEM_unused+1. And I do not want the check of a.hvmmem_type
> >> against HVMMEN_unused later in this routine appear in that patch.
> >>
> >>>> That might have been slightly cleaner; but we're going to have to put it
> >>>> back as soon as the development window opens anyway, so I don't really
> >>>> see the point of going through the effort of respinning the patch again.
> >>>>
> >>>> Would you be willing to ack this version anyway?
> >>> I have no problem doing so (and in fact I have it on my to by
> >>> committed list already), it is just looked slightly confusing (and
> >>> I had already typed half a reply that this isn't what was discussed
> >>> until I properly looked at the next hunk), and hence I wanted to
> >>> understand the motivation. And btw., I'm not convinced it would
> >>> need to be put there anyway later: I don't view the used
> >>> mechanism as a good (read: extensible) one to deal with what
> >>> would be holes in the array above. Indeed we can't leave them
> >>> uninitialized (as that would mean p2m_ram_rw), but I think we
> >>> should better find a way to initialize _all_ unused slots without
> >>> requiring an initializer for each of them. Sadly the desire to allow
> >>> compilation with clang prohibits the most natural solution:
> >>>
> >>>        static const p2m_type_t memtype[] = {
> >>>            [0 ... <upper-bound> - 1] = p2m_invalid,
> >> Not sure if this will compile? Can have a try. :)
> >>
> > To answer your question this can compile with gcc but not probably not
> > with clang. This syntax is gcc extension.
> >
> > See: https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
> 
> That syntax works in Clang, but will subsequent entries in the list will
> suffer a -Werror,-Winitializer-overrides and fail to compile.
> 

This can easily be fixed :-)

 [ 0 ... <first-upper-bound> ] = p2m_inavlid;
 [ <second-lower-bound> ...  <second-upper-bound> ] = p2m_invalid;

But I'm not sure whether you guys think this is pretty or ugly.


Wei.

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